A charged particle beam apparatus is an apparatus for acquiring an image of a sample by irradiating the sample placed in a sample chamber which is maintained in a relatively high vacuum state with a charged particle beam. For example, in a scanning electron microscope or a transmission electron microscope, a target sample is irradiated with an electron beam as a charged particle beam, and a microscopic image of the target sample is generated based on the amount of secondary electrons or transmitted electrons detected by a detector.
In such a charged particle beam apparatus, an ion pump is used to maintain the interior of the sample chamber where a sample is placed or the interior of a lens barrel of a charged particle optical system in a high vacuum state. When the set vacuum state is to be measured using the ion pump, a current to be detected becomes weak, and thus the influence of noise cannot be ignored.
As a method for solving the problem of noise as described above, Patent Literature 1 discloses “a leakage parabolic voltage leaked from a parabolic voltage generation circuit to an operational amplifier of a pulse width control circuit via a high voltage resistance circuit is cancelled by adding a divider parabolic voltage of the same amplitude and the same phase as the leakage parabolic voltage to the operational amplifier and performing differential amplification, the divider parabolic voltage being obtained by resistor-dividing the parabolic voltage of the parabolic voltage generation circuit”.